1. Field of the Invention
The present invention is directed to radical-curable adhesive compositions which include a (meth)acrylate component; a coreactant selected from unsaturated cyclic, bicyclic and tricyclic (meth)acrylates and epoxidized alkyl, cycloalkyl, bicyclic and tricyclic (meth)acrylates; and a radical cure-inducing composition. Reaction products of the compositions of this invention exhibit superior resistance to thermal degradation.
2. Brief Description of the Technology
Radical-curable adhesive compositions generally are well-known. In the context of anaerobic adhesives, see e.g., R. D. Rich, "Anaerobic Adhesives" in Handbook of Adhesive Technology, 29, 467-79, A. Pizzi and K. L. Mittal, eds., Marcel Dekker, Inc., New York (1994) and references cited therein. In the context of radiation-curable adhesives, see e.g., J. G. Woods, "Radiation Curable Adhesives" in Radiation Curing: Science and Technology, 333-98, S. P. Pappas, ed., Plenum Press, New York (1992).
Uses of radical-curable adhesives are legion and new applications continue to be developed.
In the past, many adhesives particularly anaerobic adhesives, have been rendered resistant to degradation at elevated temperatures by the inclusion of certain additives.
For instance, U.S. Pat. No. 3,988,299 (Malofsky) refers to a heat curable composition having improved thermal properties, which includes certain acrylate monomers and maleimide compounds.
L. J. Baccei and B. M. Malofsky, "Anaerobic Adhesives Containing Maleimides Having Improved Thermal Resistance" in Adhesive Chemicals, 589-601, L-H, Lee, ed., Plenum Publishing Corp. (1984) report the use of maleimides--specifically, N-phenyl maleimide, m-phenylene dimaleimide and a reaction product of methylene dianiline and methylene dianiline bismaleimide--to increase the thermal resistance of anaerobic adhesives which are fully cured at temperatures of at least 150.degree. C.
While the addition to radical-curable adhesive compositions of such maleimide compounds to render them resistant to thermal degradation provides reaction products with acceptable performance, it would be desirable to find alternative compounds to include in such formulations. Moreover, maleimides are known to inhibit photoinitated cure of acrylate-based compositions.
Compositions containing both epoxy resins and (meth)acrylate resins are known. For instance, U.S. Pat. No. 5,656,703 (Costin) refers to curable compositions, particularly well-suited for coating applications, containing an epoxy resin, a poly(meth)acrylate, a metal di(meth)acrylate as an adhesion promoter and a polyamine as a curing agent.
In addition, monomers containing both acrylate groups and epoxy groups are known generally.
For instance, U.S. Pat. Nos. 5,468,886 (Steinmann) and 5,599,651 (Steinmann) relate to radiation-sensitive (cyclo)aliphatic epoxy compounds containing both acrylate groups and (cyclo)aliphatic epoxy groups. These compounds are positioned as being useful in stereolithographic applications and useful as photocurable adhesives when a photoinitiator is added to the compounds.
U.S. Pat. No. 5,395,566 (Kobayakawa) refers to photochromic compositions containing, in addition to a photochromic compound, compounds having both radical-polymerizable groups and epoxy groups.
U.S. Pat. No. 5,326,827 (Aoki) refers to heat-curable resins comprising an acrylic polymer with epoxide and hydroxyl functionality, a polyfunctional epoxide compound, and a heat-latent cationic polymerization initiator.
And curing agents for epoxy-containing compounds are known, such as those commercially available from Ajinomoto Co., Tokyo, Japan under the tradename "AJICURE", for instance, "AJICURE" PN-23. See U.S. Pat. No. 4,546,155 (Hirose).
Notwithstanding the state-of-the-technology, there is an on-going search for additives to improve the thermal performance of reaction products of radical-curable adhesives. In addition, it would be desirable from a commercial, economic, environmental, supply and regulatory standpoint to provide alternatives and/or replacements for maleimide-type materials for improving the resistance to thermal degradation of reaction products of radical-curable adhesive compositions.